It says in the text thatthe round lateral push-buttonon the lock plate acted as a trigger that would release the cocked serpentine, making it snap forward and get the piece of glowing tinder in touch with the powder on the igniting pan.

In Barcelona in 1529 over eight thousand [8270] troops embarked to accompany the emperor on his trip to Italy. We know from René Quatrefages - "La revolución militar moderna. El crisol español" / Modern Military Revolution, the Spanish melting pot - that among the shooters had "escopeteros" and "arcabuceros" or arquebusiers. For example, the company of Diego de Andrade, 279 soldiers, had 81 arquebusiers and escopeteros 27. The arcabucero charged more than the "escopetero".
I've been intrigued for years - no kidding - about the difference between escopetas and arquebuses, and assumed that the difference was calibers, but I also thought that there might be differences in the mechanisms triggering or in the material they were made: brass or iron.
The word "escopeta" is used in Spain regularly since 1508 - was previously used "espingarda" - and it seems the term was adopted in Italy from the word "schiopetta" but involving the same weapon. But clearly were different weapons, for two categories of soldiers resulted.

I add an image to display further details and questions. The arquebus red circle, has no key.I understand that you mean alock mechanism,
instead of key.

Is it fired with fuse? Sure, as it did not have a lock mechanism it had to be fired using either a fuse/match or an igniting iron.

In the tails of the arquebuses with red circle you can see a piece. In the arquebuses of the German soldiers not appear

As I said, and will show soon, those butts have a trap, a recess with a sliding wooden cover; it was NOT a "patchbox" but was used to keep small cleaning utensils, like a worm and scourer, and wadding for the load.
Please see an Italian arquebus of ca. 1525-30, with a butt trap on the underside of the buttstock in which the original cleaning tools are still preserved; in The Michael Trömner Collection:http://www.vikingsword.com/vb/showt...hlight=arquebus